I could find only one book, Programming Crystal. It looks nice, but it is more than 2 years old. I don’t know how much the language has changed since the book was written.
Is it still the best book for Crystal? Are there any other books/video courses?
https://www.packtpub.com/product/crystal-programming/9781801818674 I can recommend it, it goes quickly over the basics and then as a good focus on advanced topics like c bindings and meta programming. I also like the last chapters which focus on how to layout projects.
Crystal Programming: A project-based introduction to building efficient, safe, and readable web and CLI applications. Thats a really fine book to learn crystal